The present invention is an improved method for hydrolyzing chlorosilanes having at least three chlorine atoms bonded to each silicon atom to form silicone resins. The method comprises adding at least one of hydridochlorosilane, tetrachlorosilane, or organochlorosilane to a two-phase mixture comprising a non-polar organic solvent, an aqueous phase comprising 0 to about 43 weight percent hydrochloric acid, and a surface active compound selected from the group consisting of alkylsulphonic acid hydrate, alkali metal salt of alkylsulphonic acid, arysulphonic acid hydrate, and alkali metal salt of arylsulphonic acid.
It is well known in t he prior art that halosilanes readily hydrolyze in the presence of water to form silanols which condense to form polysiloxanes. Furthermore, it is well known that these two processes occur almost simultaneously when the halosilane contains three or more halogen atoms. The result of this rapid hydrolysis and condensation is an insoluble gel which is of little practical value. See, for example, Boldebuck, U.S. Pat. No. 2,901,460.
Numerous solutions to the above problem have been suggested. Boldebuck, supra, described for instance utilizing a hydrolysis medium comprising tetrahydrofuran and water to alleviate the gelling. Frye et al., U.S. Pat. No. 3,615,272 describe a process for forming hydrogensilsesquioxane resin comprising reacting a silane in a hydrocarbon solvent with sulfuric acid and an aromatic hydrocarbon, washing the reaction mixture with water and sulfuric acid until neutral and recovering the product by evaporation of the solvent.
Bank et al., U.S. Pat. No. 5,010,159, teach a method of hydrolyzing hydridosilanes with 2 or more hydrolyzable groups which comprises forming an arylsulfonic acid hydrate containing reaction medium, adding the silane to the reaction medium, facilitating hydrolysis of the silane to form the polyester, and recovery of the polymer. It is taught that the arylsulfonic acid hydrate containing reaction medium can be formed either by dissolving an arylsulfonic acid hydrate in a solvent, such as an alcohol, or it can be generated by the preferred method of reacting an aromatic hydrocarbon with concentrated sulfuric acid.
Ezerets et al., SU (11) 1147723, teach a method of hydrolysis of methylchlorosilane alone or as a cohydrolysis with diorganodichlorosilanes or organotrichlorosilanes, with a functionality of 2.9 to 3 in a mixture of an aromatic hydrocarbon solvent and a water-miscible solvent. The method is characterized by the water-miscible solvent comprising acetic acid and concentrated hydrochloric acid and the presence of a water-soluble cationic surfactant. The water-soluble cationic surfactants are described as amine hydrochlorides, quaternary ammonium salts, and salts of protonated carboxylic acids, which contain 6 to 20 carbon atoms.
Hacker et al., WO 98/47941, describe a process for preparing hydridosiloxane and organohydridosiloxane resins. The process involves the steps of contacting a silane monomer with a phase transfer catalyst in the presence of a reaction mixture that includes a nonpolar solvent and a polar solvent. Hacker et al. state that the phase transfer catalysts are quaternary ammonium salts.
Shkolnik et al., SU (11) 1666469, describe a process for preparation of oligoorganohydridosiloxanes comprising conducting an acid hydrolysis of a mixture of phenyltrichlorosilane or vinyltrichlorosilane, dimethyldichlorosilane, and hexamethyldisiloxane in the presence of a sulfonated copolymer of divinylbenzene and styrene.
It is also known that nonionic surface active agents can effect the hydrolysis of diorganochlorosilanes. For example, Williams, U.S. Pat. No. 4,412,080, teaches that cyclic dimethylpolysiloxanes can be prepared by hydrolysis of dimethyldichlorosilane and aqueous hydrochloric acid in the presence of a normal C.sub.6-16 alkyl sulfonic acid to give good yields of cyclic polysiloxanes.
The present invention is a process for producing silicone resins in high yield which are readily soluble in non-polar solvents. The method has the advantage of (1) not requiring the use of sulfuric acid, (2) not having the solvent be a reactant in the system as when the solvent is reacted with sulfuric acid to form an arylsulfonic acid hydride, thereby making the process easier to control, (3) having the hydrogen chloride generated by the hydrolysis of the chlorosilanes separate from the mixture as an anhydrous gas and thus is in a form in which it can be recycled to the method or otherwise used, and (4) allowing the aqueous layer containing the hydrochloric acid and the surface active agent to be directly recycled back into the method.
Resins prepared by the present method are unique in that for a given monomer distribution at a similar percent solids, they tend to favor a high degree of intramolecular cyclization relative to resins prepared by other procedures. Additionally, thin films of cured resins prepared by the present method can have high resistance to environmental induced stress cracking.
Polymers formed by the present method have excellent coating and sealing characteristics when cured to their ceramic or ceramic-like state. Such polymers have utility, for example, in coating electronic devices to form protective barriers.